Solution 19: Fibonacci数列

public class Fibonacci {
	public int getNthElemRec(int n) {
		if (n <= 0) {
			return -1;
		}
		if (n <= 2) {
			return 1;
		}
		return getNthElemRec(n - 1) + getNthElemRec(n - 2);
	}

	public int getNthElemNoRec(int n) {
		if (n <= 0) {
			return -1;
		}
		if (n <= 2) {
			return 1;
		}
		
		int a = 1, b = 1;
		int res = 0;
		
		while (n >= 3) {
			res = a + b;
			a = b;
			b = res;
			--n;
		}
		
		return res;
	}
}